bug#9990: valgrind warning in add_row_entry

[Eli Zaretskii <eliz@gnu.org>]

> Date: Fri, 11 Nov 2011 17:30:58 +0200
> From: Eli Zaretskii <eliz@gnu.org>
> Cc: 9990@debbugs.gnu.org
> 
> However, I spotted something strange related to the call to
> row_equal_p, here:
> 
>   /* Skip over rows equal at the bottom.  */
>   i = last_new;
>   j = last_old;
>   while (i - 1 > first_new
>          && j - 1 > first_old
>          && MATRIX_ROW (current_matrix, i - 1)->enabled_p
> 	 && (MATRIX_ROW (current_matrix, i - 1)->y
> 	     == MATRIX_ROW (desired_matrix, j - 1)->y)
> 	 && !MATRIX_ROW (desired_matrix, j - 1)->redraw_fringe_bitmaps_p
>          && row_equal_p (MATRIX_ROW (desired_matrix, i - 1),
>                          MATRIX_ROW (current_matrix, j - 1), 1))
>     --i, --j;
> 
> Some of these conditions use incorrect indices to access the glyph
> matrices: `i' should be used for the current matrix and `j' for the
> desired matrix.  Some of these conditions use `i' and `j' correctly,
> some don't.

Below is a patch I intend to install, if no one finds any thinko in
it.  Dan, can you try this and see if it resolves the valgrind
complaints (assuming you can reproduce them)?

=== modified file 'src/dispnew.c'
--- src/dispnew.c	2011-10-08 10:58:50 +0000
+++ src/dispnew.c	2011-11-11 15:53:27 +0000
@@ -4334,10 +4334,10 @@ scrolling_window (struct window *w, int 
   j = last_old;
   while (i - 1 > first_new
          && j - 1 > first_old
-         && MATRIX_ROW (current_matrix, i - 1)->enabled_p
-	 && (MATRIX_ROW (current_matrix, i - 1)->y
-	     == MATRIX_ROW (desired_matrix, j - 1)->y)
-	 && !MATRIX_ROW (desired_matrix, j - 1)->redraw_fringe_bitmaps_p
+         && MATRIX_ROW (current_matrix, j - 1)->enabled_p
+	 && (MATRIX_ROW (current_matrix, j - 1)->y
+	     == MATRIX_ROW (desired_matrix, i - 1)->y)
+	 && !MATRIX_ROW (desired_matrix, i - 1)->redraw_fringe_bitmaps_p
          && row_equal_p (MATRIX_ROW (desired_matrix, i - 1),
                          MATRIX_ROW (current_matrix, j - 1), 1))
     --i, --j;